1. Field of the Invention
The invention relates to software architectures for networked computing devices, which are operated in heterogenous network environments and are able to adapt to varying content types.
2. Discussion of the Related Art
Today, most operating environments are still focused on general purpose desktop computers, and are tightly coupled to their underlying operating systems, a typical example being Microsoft Windows. For certain information device categories, there exist specialized environments like Epoch (cell phones) and Palm OS (Palm PDAs). Several technologies exist which can be utilized in different, cross-platform environments (e.g. Personal Java VMs). These systems so far do not provide the desire degree of:                portability (different HW architectures)        scalability (different speed, memory, formfactors)        integration (no redundant components, functions)        extensibility (update/install of SW components via network to adapt to new content types)for coping with today's rapidly changing device categories and content types. In particular, large device vendors are sought after for a common software infrastructure which is flexible enough to serve the needs of very different, special purpose, and usually resource-constrained devices.        
Most existing drivers focus on expensive desktop-oriented windowing systems (Windows, X etc.), and accelerated display hardware. Consequently, these drivers have a high degree of runtime configurability (color depth, screen resolution), and use a design which assumes that most performance critical functions can be offloaded to special purpose hardware (bit block transfers, line drawing etc.). Inherently, such a design exhibits a considerable amount of indirection (functions called via pointers), which is acceptable if this overhead is compensated by fast graphics hardware. There are some adaptations of such drivers for generic framebuffer devices, but because of the display hardware oriented design, they do not make use of platform specific optimization mechanisms.
In general, applications use toolkit library functions, which in turn map to driver functions, either by means of direct calls or some inter-process communication mechanism. The driver then branches according to the display HW type (display processor), the user configured screen resolution (width, height) and color depth, invoking the functions which actually do the work (mostly by delegating it to the display processor).
Embedded computing devices mostly don't have accelerated display HW, and provide just a framebuffer memory area. They usually have a fixed resolution and color depth, i.e. don't have a high degree of runtime configurability. They mostly have RISC like processors which provide efficient mechanisms for memory block transfers (number of registers). It is desired to have a graphics rendering mechanism for use with an embedded device which is designed to compensate for a lack of expensive display hardware.
To be suitable for global deployment, it is desired to be able to use local font sets. To overcome the problem of various different, and partially conflicting character encoding schemes, the Unicode initiative has become a de-facto standard. It is based on multi-byte character encoding and as of today contains about 50,000 character symbols.
This constitutes a considerable problem for displaying unicode text with conventional font rendering systems. In general, a font object includes of a collection of per-font and per-character attribute values, the character attributes being index-accessed (with the character code) for efficiency reasons.
The per-character attribute (width, bearing, glyph etc.) implementations usually use arrays of the size of the required character set. While this involves just about 10 kB for a bitmapped 256-character font instance (e.g. ASCII), a full unicode font (50,000 characters) would use up to 2 MB for a single instance (face/weight/slant/size). Typical applications (e.g. web-browsers) utilize about 4 different instances, adding up to 8-10MB of required font space. This amount of memory is not generally available for embedded devices (16 MB RAM/ROM). It is therefore desired to have a font extension mechanism which permits the implementation of a reasonable number of font instances in less than,e.g., 2 MB of memory.
In order to provide a suitable basis for a broad range of applications for use with embedded devices, it is recognized herein that it would be advantageous to implement a full windowing system with z-order capabilities (i.e. windows can overlap, with foreground windows partially or fully obscuring background windows). In addition, the rendering mechanism should support explicitly set, non-z-order implied clipping rectangles. Devices having special display processors may implement this by means of HW-augmented region clipping. As mentioned above, embedded devices usually do not have special display processors. It is desired to provide an embedded device with a rendering mechanism that supports explicitly set, non-z-order implied clipping rectangles.
Handwriting recognition systems known in the art include the GRAFFITI system, developed by Xerox, which is used in the PalmPilot, and the JOT system, which is used in WinCE (and others). It is desired to have an improved handwriting recognition system, particularly for use with an embedded computing device.